There isn't any official mechanism for "backordering" a domain. You can go on a waiting list with a company. They will check the domain when it expires and if it's not renewed, they will TRY to buy it for you... but even then, you aren't guaranteed to get the domain because someone else might have "backordered" it from a different web domain company (and so the two domain companies are racing to buy the domain for their customer). If there were only one company selling domains, then sure, backordering might be a guarantee that you'll get it if it's not renewed... but with tons of domain sellers out there, "backordering" a domain doesn't guarantee anything.
